A known variable valve timing control apparatus described in JP2006-348296A (hereinafter referred to as Reference 1, with reference to paragraphs 63 to 76, FIG. 7, and FIGS. 15 to 19) includes a first fluid control valve, a first phase restriction portion, a second phase restriction portion, and a second fluid control valve. The first fluid control valve controls supply and discharge of a hydraulic fluid to and from a fluid pressure chamber to thereby rotate a driven rotor relative to a driving rotor. The first phase restriction portion restricts a relative rotational phase of the driven rotor to the driving rotor within a first restriction range ranging from a predetermined phase between a most advanced angle phase and a most retarded angle phase to a phase located toward a retarded angle side from the predetermined phase. The first phase restriction portion releases the relative rotational phase from the first restriction range. The second phase restriction portion restricts the relative rotational phase within a second restriction range ranging from the predetermined phase to a phase located toward an advanced angle side from the predetermined phase. The second phase restriction portion releases the relative rotational phase from the second restriction range. The second fluid control valve for the first and second phase restriction portions controls the supply and discharge of the hydraulic fluid to and from the first and second phase restriction portions.
The first phase restriction portion includes a first restriction member and a first restriction groove formed in the driven rotor. The first restriction member protrudes from the driving rotor toward the driven rotor into the first restriction groove and retracts from the first restriction groove toward the driving rotor. When the first restriction member protrudes into the first restriction groove, the relative rotational phase is restricted within the first restriction range. The second phase restriction portion includes a second restriction member and a second restriction groove formed in the driven rotor. The second restriction member protrudes from the driving rotor toward the driven rotor into the second restriction groove and retracts from the second restriction groove toward the driving rotor. When the second restriction member protrudes into the second restriction groove, the relative rotational phase is restricted within the second restriction range. When the first restriction member and the second restriction member simultaneously protrude into the first restriction groove and the second restriction groove, respectively, the relative rotational phase is restricted in the predetermined phase between the most advanced angle phase and the most retarded angle phase.
According to the aforementioned configuration described in Reference 1, the relative rotational phase is released from the first restriction range and the second restriction range after the first restriction member and the second restriction member retract from the first restriction groove and the second restriction groove, respectively. Thereafter, even when the relative rotational phase shifts toward the retarded angle side and the second restriction member is dislocated from a position facing the second restriction groove, the first restriction member may face the first restriction groove. At this time, the hydraulic fluid is discharged from the first restriction groove to thereby protrude the first restriction member into the first restriction groove. That is, the relative rotational phase may be restricted within the first restriction range. Thus, the second fluid control valve for the first and second phase restriction portions is only controlled to restrict the relative rotational phase in the predetermined phase and in a phase between the predetermined phase and the most retarded angle phase.
Under a condition where an internal combustion engine is started in a cold condition, a relative rotational phase of a driven rotor relative to a driving rotor is located between a most advanced angle phase and a most retarded angle phase, for example, in a variable valve timing control apparatus arranged at a suction system. That is, the relative rotational phase is positioned in a boundary phase where the internal combustion engine may appropriately start. When the relative rotational phase is restricted in a predetermined phase located toward an advanced angle side from the boundary phase, hydrocarbon emissions may be reduced for several tens of seconds right after the start-up of the internal combustion engine. However, the internal combustion engine continues idling and warms up while the relative rotational phase is maintained in the predetermined phase, resulting in an increase of the hydrocarbon emissions. According to the configuration described in Reference 1, the relative rotational phase may be restricted in a phase located toward a retarded angle side from the predetermined phase; thereby, the hydrocarbon emissions are reduced. As a result, the variable valve timing control apparatus described in Reference 1 controls the relative rotational phase depending on operating conditions of the internal combustion engine.
In addition, a variable valve timing control apparatus disclosed in JP2009-74384A (hereinafter referred to as Reference 2) includes a fluid control valve controlling supply and discharge of a hydraulic fluid to a fluid pressure chamber to thereby rotate a driven rotor relative to a driving rotor, a lock mechanism locking a relative rotational phase of the driven rotor to the driving rotor within a predetermined phase between a most advanced angle phase and a most retarded angle phase and releasing the relative rotational phase from the predetermine phase, and a biasing mechanism (spring) biasing the driven rotor toward an advanced angle side. A biasing force of the biasing mechanism is limited in a range ranging from a phase between the most retarded angle phase and the predetermined phase, to the most retarded angle phase.
According to the configuration disclosed in Reference 2, after a restricted state of the relative rotational phase is released, for example, when the relative rotational phase shifts to the phase between the most retarded angle phase and the predetermined phase, the biasing force of the spring acts on the driven rotor to restrict the relative rotational phase in the phase. That is, even when the variable valve timing control apparatus does not include a restriction mechanism having a restriction member and a restriction groove, the relative rotational phase is restricted in the phase between the most retarded angle phase and the predetermined phase.
According to the configuration disclosed in Reference 1, the first phase restriction portion and the second phase restriction portion are simultaneously controlled. Accordingly, when the relative rotational phase is released from the first restriction range and the second restriction range, the first restriction member and the second restriction member retract from the first restriction groove and the second restriction groove, respectively. As a result, when the first restriction member and the second restriction member are operated again right after the releasing of the relative rotational phase, for example, whether or not the first restriction member is restricted in the first restriction range depends on whether or not the first restriction member faces the first restriction groove. In the case where viscosity of the hydraulic fluid is high, for example, right after the internal combustion engine is started, the timing may not be matched between a phase control of the first fluid control valve and a restriction control of the second fluid control valve to cause the first restriction member to be dislocated from a position facing the first restriction groove. In such case, the relative rotational phase may not be restricted in the first restriction phase.
Moreover, according to the configuration explained in Reference 2, the restriction of the relative rotational phase depends on the biasing force of the spring. Accordingly, precision for the setting and arrangement of the spring is required. Further, as a considerably large spring force is not set, the relative rotational phase may not be surely restricted. Furthermore, when the biasing force of the spring excessively increases, an excessive load may be generated in a displacement of the relative rotational phase rotating in a usual operation of an internal combustion engine.
A need thus exists for a variable valve timing control apparatus, which is not susceptible to the drawback mentioned above.